For the past 2 weeks my PC has been down. It started getting a black screen without any notification. Not the known Blue Screen of Death but just black. The fans kept on running and everything seemed powered on. My PSU is a Cooler Master RS-620 620W. Sometimes it would just give up within a couple of minutes while examining the BIOS setup screens, other times it would last 15-0 minutes but mostly less than that. My system is an Intel DX58SO motherboard with an Intel i7-920 processor and the latest BIOS. The case has several (3-4) fans in addition to the CPU fan, the bridge (?) fan near the CPU and the video card fan.

It is not a software (OS) problem because this happens regardless of what I use: Windows 7 Ultimate 64-bits (hard disk), Ubuntu Linux 12.04 (Live CD) or motherboard's BIOS setup screens.

I thought it was the memory so I removed my DDR3 and bought a new single 4GB module (DX58SO motherboard) but same problem.

Just for the sake of problem solving I tried the monitor on another computer but it worked fine for hours without issue.

I began to think my nVidia GTX285 had kicked the bucket (204W) so I removed it and bought a new low profile nVidia GT210 card which consumes only 30W, Unfortunately the problem persists.

I was told perhaps it was a heat transfer problem between the CPU and the HSF. Since my room temperature (with fan) is about 28-29 Celsius I decided to run a new test by turning on the air conditioner, when the room temperature was 25 Celsius I turned on a portable fan (used for people) to point directly at the CPU as the case is open. In this setup I managed to use the system for more than 3 hours without incident. I turned it off as I considered it stable.

Then I unmounted the CPU HSF, cleaned it up again, removed the old termogel that was already dried (was like dust), cleaned both surfaces with alcohol and let it rest for a few hours. Then I reapplied thermo conducting gel (Arctic Silver). I let it rest overnight.

This morning I let the open case, turned on the fan pointing at the CPU (the CPU also has its HSF installed) and turned on the system without air conditioning, my room temperature was 28 Celsius with ceiling fan. I was hoping that would solve my predicament, unfortunately at the 8 minute mark the screen turned black but everything seemed powered up.

I am running out of options, I have been buying new parts that I can almost build a new system. At the moment I don't know if perhaps the problem is the Intel CPU, have doubts it is a PSU problem (620W) but maybe it is the Intel DX58SO motherboard, but then if it was then I don't think the airco test wouldn't have reached the 3 hour mark.

Any ideas? this is my workhorse and I need it for both development and simulation, I need it running on my tropical environment. It ran fine in this conditions for about 2 years.

For the sake of ruling out mere chance I ran the test again with the system in an air conditioned room at 24 Celsius (pretty cool) using the low power (30W) brand new video card instead of the original 204W card (nvidia GTX285). The two HDD are disconnected but I either use the BIOS setup screen (view) or boot a Live Ubuntu 12.04 Linux CD on the ATAPI (set as boot device).

Unfortunately the problem persists even at cool temperatures. First the screen goes totally black BUT I notice that both the front panel HDD (Hard Disk Drive) and motherboard HDD activity LEDs are flashing. Do note the HDD are not connected, the DVD/CD LED is not flashing anymore so there is no access to the Live CD, it appears as if the system was trying to access the hard disk for something. I don't know why because the system is not configured for auto sleep nor suspend (desktop) and because I am using the system browsing internet and NOT doing anything that would initiate a Suspend (deliberate or due to inactivity).